AIRLINE pilots fear their jumbos could be shot down by conspiracy theorists who believe they are being poisoned by commercial aircraft.

The conspiracy theorists are part of a global "chemtrail" movement that claims jets are spraying toxic chemicals over heavily-populated towns and cities around the world.

"Threats to shoot down aircraft or harming pilots are becoming more prevalent, overt and alarming," says Mike Glynn, a current airline captain and former vice-president of the Australian and International Pilots Association.